Volt

Electromagnetic Compatibility Description

Vehicles are typically subject to certain legal requirements that limit the amount of electromagnetic interference (EMI) that can be generated by the vehicle's electronic devices. Additionally, the electronic devices within the vehicle must be able to withstand a certain amount of EMI without affecting their operation. EMI is generated whenever electrical current flows through a circuit. The amount of EMI generated, or amplitude, is usually dependant upon the amount of current flow, amperage, the on-off pattern of current flow through the circuit and frequency. The EMI requirements are generally referred to as electromagnetic compatibility.

There are many ways of ensuring the vehicle meets electromagnetic compatibility requirements. These include:

The power inverter module, often referred to as the drive motor generator power inverter module, and the 14 V power module, also called the accessory DC power control module assembly, each contain filter capacitors connected to the high-voltage circuits. These capacitors are necessary to reduce the voltage spikes that occur as a result of the switching of current On and Off. Reducing voltage spikes reduces EMI. The frequency of current switching is also closely regulated. Too high a frequency can cause an increase in EMI generation.

Different types of wire/cable shielding methods are utilised in the vehicle. Common types of circuit shielding include twisted-pair and internal braid or foil. Twisted pairs are typically used in circuits such as serial data circuits. The wire pair is twisted together at a particular turns-per-length ratio. Shielded cable is utilised for all other circuits requiring either protection from external EMI or to reduce EMI radiation of the cable itself into other nearby components or circuits.

The high-voltage cables utilise internal braid shielding. Typically, both ends of the internal braid shield are attached to chassis earth. All of the high-voltage, internally shielded cables are earthed at their cable end attachment points. Mounting blocks, where used, perform the shield to chassis earth connection. Connection points not serviced with a mounting block utilise a separate ring terminal.

The signal circuits for the transmission sensors utilise shielding protection. The drive motor generator position sensor and temperature sensor circuits utilise internal foil shielding. The wiring harness external of the transmission assembly is connected to chassis earth with ring terminals at the drive motor control module assembly. The internal transmission wiring harness is attached to chassis earth with a ring terminal at the valve body assembly.

The auxiliary transmission fluid pump 3 phase cables utilise internal foil shielding. The wiring harness shield is connected to chassis earth within the motor generator power inverter module.

Certain components utilise their structure to effectively shield EMI. Metal covers, chassis earthed metal cases and electro-magnetically conductive gaskets may all be part of a component's electromagnetic compatibility design.

A loss of proper shielding may result in poor AM band radio reception and/or incorrect sensor circuit readings depending upon the location of the shield loss. Damage that has penetrated to the insulated conductor of high voltage cables is not repairable. Minor damage to the outer sheathing can be repaired, refer to Drive Motor Generator Power Inverter Module Cable Inspection . Certain Low and Intermediate voltage shielded wiring harnesses may be repairable. Refer to Wiring Repairs and Splicing Twisted or Shielded Cable .